1. Field of the Invention
This present invention relates generally to techniques for performing wellsite operations. More specifically, the present invention relates to techniques for preventing blowouts, for example, involving severing a tubular at the wellsite.
2. Description of Related Art
Oilfield operations are typically performed to locate and gather valuable downhole fluids. Oil rigs are positioned at wellsites, and downhole tools, such as drilling tools, are deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore (or borehole) to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubulars (or tubular strings) may be positioned in the wellbore to enable the passage of subsurface fluids to the surface.
Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. Equipment, such as blow out preventers (BOPs), are often positioned about the wellbore to form a seal about a tubular therein to prevent leakage of fluid as it is brought to the surface. Typical BOPs may have selectively actuatable rams or ram bonnets, such as pipe rams (to contact, engage, and encompass tubulars and/or tools to seal a wellbore) or shear rams (to contact and physically shear a tubular), that may be activated to sever and/or seal a tubular in a wellbore. Some examples of BOPs and/or ram blocks are provided in U.S. patent application Ser. Nos. 4,647,002, 6,173,770, 5,025,708, 5,575,452, 5,655,745, 5,918,851, 4,550,895, 5,575,451, 3,554,278, 5,505,426, 5,013,005, 5,056,418, 7,051,989, 5,575,452, 2008/0265188, 5,735,502, 5,897,094, 7,234,530 and 2009/0056132. Additional examples of BOPs, shear rams, and/or blades for cutting tubulars are disclosed in U.S. Pat. Nos. 3,946,806, 4,043,389, 4,313,496, 4,132,267, 4,558,842, 4,969,390, 4,492,359, 4,504,037, 2,752,119, 3,272,222, 3,744,749, 4,253,638, 4,523,639, 5,025,708, 5,400,857, 4,313,496, 5,360,061, 4,923,005, 4,537,250, 5,515,916, 6,173,770, 3,863,667, 6,158,505, 4,057,887, 5,178,215, and 6,016,880. Some BOPs may be spherical (or rotating or rotary) BOPs as described, for example, in U.S. Pat. Nos. 5,588,491 and 5,662,171, the entire contents of which are hereby incorporated by reference herein.
Despite the development of techniques for addressing blowouts, there remains a need to provide advanced techniques for more effectively severing a tubular within a BOP. The invention herein is directed to fulfilling this need in the art.